Anisotropic larval connectivity and metapopulation structure driven by directional oceanic currents in a marine fish targeted by small-scale fisheries

The dispersal during the planktonic larval period is a key feature to understand the metapopulation structure of marine fishes, and is commonly described by four general models: (1) lack of population structure due to extensive larval dispersal; (2) isolation by geographic distance, where larval connectivity decreases with increasing distance between sites in all directions (isotropy); (3) population structure without any clear geographic trend (chaotic); and (4) population structure explained by seascape approaches that explicitly incorporate the spatial and temporal variations in the direction and strength of oceanic currents via oceanographic modeling. We tested the four models in the Pacific red snapper Lutjanus peru, a key commercial species in the Gulf of California (GC), Mexico. We genotyped 15 microsatellite loci in 225 samples collected during 2015–2016 from 8 sites, and contrasted the observed empirical genetic patterns against predictions from each model. We found low but significant levels of population structure among sites. Only the seascape approach was able to significantly explain levels of genetic structure and diversity, but exclusively within spring and summer, suggesting that this period represents the spawning season for L. peru. We showed that in the GC, the strong asymmetry in the oceanic currents causes larval connectivity to show different values when measured in distinct directions (anisotropy). Management tools, including marine reserves, could be more effective if placed upstream of the predominant flow. Managers should consider that oceanographic distances describing the direction and intensity of currents during the spawning period are significant predictors of larval connectivity between sites, as opposed to geographic distances.